1. Field of the Invention
This invention relates in general to timekeeping, and more specifically to the rapid and facile determination of the effective local civil time for any specific geographical location in the world. The invention, in particular, addresses this, while automatically accounting for Daylight Saving Time adjustments that may be effected in any particular locale.
2. Description of the Prior Art
It is well known in the art to provide a clock that simultaneously displays the time across various, if not all, time zones around the world. The word “Clock” as used herein is meant to include all forms of timepieces or means for recording and displaying the passage of time. As such, a clock represents a dynamic display. Corresponding times within different world time zones may also be presented graphically in a static format.
(Conventional Clock Dials in General)
The representation of time on a standard dial clock's face is often thought to trace back to early people's familiarity with sundials. In the most common design of sundial, a graduated time scale in imprinted on a horizontal surface, which is then aligned in a direction facing along the line between true North and South. A shadow-casting style or gnomon is arranged with respect to the graduated surface, such that the shadow caused by the relative movement of the sun throughout the day will fall upon and intercept the graduated time scale and indicate the local solar time.
While a sundial can be made very accurate and precise in the determination of solar time for a given locale, it can only be useful if and when the sun is sufficiently bright to cast a distinct shadow. This rather severe operational limitation has led throughout history to the invention of dial clocks which substituted a mechanical movement driving an indicator hand to substitute for the moving shadow of the sun. As the mechanical clock's hand or hands were intended to be an analogue or metaphor for a solar shadow, mechanical dial clocks have most commonly moved the indicator hand or hands in the same direction the gnomon shadow moves on a sundial throughout the day. This is the direction that we now commonly call clockwise.
(Clock Dials Incorporating a Polar Projection.)
With the advent of the industrial age, and with improvements in the science and art of cartography, clock designers hit upon the idea of combining a presentation of the Earth's surface with a mechanical clock, in order to indicate the differing local times at various locales. Many of these approaches resulted in multi-zone world time clock designs which made use of a circular world map, centered on either the North or South pole, and which operated in a manner that is mechanically similar to that of a standard two-handed clock movement. These types of clocks typically segment the world map into the various known time zones, and provide a means to allow a user to read the local time at each time zone simultaneously.
When incorporating a polar projection world map into a standard dial clock display driven by a conventional mechanical clock movement, a South polar projection of the Earth has an advantage, apart from merely depicting the world as a circular image. In a South polar projection, the graphic presentation of the Earth may rotate clockwise in the manner of a standard dial clock with the corresponding times indicated by a fixed encircling 24 hour scale. Conversely, the adoption of a North polar projection requires either that the graphic projection rotate counterclockwise against a fixed 24-hour time scale that increases in the counterclockwise direction; or that the time scale rotates about the geographic projection This would be unnatural to the clock's observers.
One example of a mechanical clock with a North polar world map projection and counterclockwise mechanical movement can be seen in FIG. 1 of U.S. Pat. No. 5,57,173, granted in 1896 to D. W. Thompson.
The other approach, maintaining clockwise movement of a map projection centered on the Earth's South pole, can be seen in FIG. 1 of U.S. Pat. No. 5,146,436 by James B. Wright. Wright teaches of a mechanical world clock having a circular polar map which is divided into twenty-four zones. Overlying this map are twenty-four, radially extending hour indicators, each serving to indicate the local time at each individual time zone by pointing-out times on an encircling 24 hour scale. Two of these indicators are made particularly distinctive over the others, and are adjusted to correspond to a user's present geographical location and time zone. The first of the two indicators is meant to indicate the user's standard local time, whereas the second indicator, positioned adjacent to the first, is meant to represent adjusted local time, such a daylight saving time. The user is expected to know which of the indicators corresponds with appropriate, actual time in the local time zone.
One hybrid world clock design which maintains a standard clockwise hand movement and incorporates a North polar map projection is described in U.S. Pat. No. 862,884, to P. G. Connor. Connor's geographical clock makes use of a moving annular time indication scale, which has the 24 hours of the day numbered in ascending order counterclockwise. This annular scale is itself secured to the hour hand of a conventional 24 hour clockwise movement. The reverse-numbered annular scale is preferably made of a transparent material to allow for viewing the map below. The annular scale then rotates with the hour hand about the centre of the map projection, giving an indication of the local time in any area on the map.
The present inventor, Dwight Darling, has also obtained U.S. Pat. No. 5,054,008 for a mechanical or electro-mechanical movement clock with a clock face based on a modified South polar projection of the world and clockwise map movement. The geographic projection of this previous invention relies on colours to identify specific time zones and correspondingly coloured peripheral indicators are provided around the circumference of the South polar projection pointing to the exterior, fixed, 24-hour scale.
(Linear Clocks Incorporating a Mercator Projection.)
In addition to the polar projections described above, there are many multi-zone world clocks in existence which make use of a more conventional Mercator projection map of the world, segregated into the 24 or more distinct time zones, and employ various methods of displaying the local time of each individual time zone. No provision is made in the system to accommodate changes to daylight saving time.
A 1966 U.S. Pat. No. 3,232,038 to Smith, describes a mechanical multi-zone world clock which has a display consisting of a Mercator projection map of the Earth. The map is perforated with a series of window-like apertures at specific locations. An indexed display tape or film is driven by a sprocket transport at a fixed rate behind the map in order that the viewer can read time index numbers through the map's viewing windows.
In later efforts, multi-zone clocks have been designed which leverage electronic means of display in the place of mechanical systems. One example can be found in U.S. Pat. No. 6,233,204 to Chu et al., where a multi-zone clock is provided which comprises a Mercator projection of the Earth with 24 discrete display windows for the separate time zones. Each display window is furnished with a Light Emitting Diode display, which presents the local civil time in its given time zone, and a coloured symbol is applied to label countries which practice Daylight Saving Time adjustment. Viewers in such case must mentally calculate the actual time in the daylight savings time zone.
Two other U.S. Pat. Nos. 5,845,257 and 6,647,370, to Fu et al., disclose methods for assisting a user in managing events across time zones. These methods also provide a Mercator projection of the Earth, with digital readouts arrayed about the map which can be set to display the current effective civil time in a number of locations of interest. The methods describe a user interface which allows the operator to choose a time to be associated with a computer recorded event. The time may be referenced to the operator's home time zone, the local time zone, or another remote time zone.
Another electronically-based world time presentation system, U.S. Pat. No. 5,007,033 to Kubota et al., provides a Mercator projection map of the Earth, with a digital display unit positioned upon it. A series of selector push-button switches are arrayed beneath the map, with each button labeled with an index number and the name of an assigned city. When the operator activates one of the selector switches, the digital display unit presents the chosen city's index number and the local civil time for that location.
(The Issue of Daylight Saving Time.)
Regardless of the chosen map projection, it is a fact that throughout the course of the calendar year various regions around the world will adjust their local time in observance of Daylight Saving Time (DST). Not every time zone in the world, however, shifts to Daylight Saving Time during the year. The majority of North America and Europe, as well as parts of South America and Asia observe some form of Daylight Saving Time. These changes will typically involve advancing local time by one hour at one point in the calendar year and then retarding local time by one hour at a second point of the calendar year. For example, in North America, time advancement is typically carried out during the Spring, and the reduction in time is typically carried out in the Fall. In parts of Africa, however, the advancement of local time takes place in the Fall, and the reduction of local time takes place in the Spring.
When the local time of certain regions of the world is advanced, or reduced as a result of Daylight Saving Time, clocks displaying world time typically must accommodate such changes in order to correctly display local time across each time zone, or be inaccurate. The usefulness of these types of clocks may be greatly diminished if such an accommodation cannot be made.
The situation is made even more complicated because some time zones are on the half-hour. For example, the time zone for Newfoundland Canada is only a half hour earlier than the time zone for the Canadian Maritime provinces. Similar instances occur in respect of other regions around the world.
A further complication is that there are standard time zones in the world wherein only a portion of the territory of such standard time zones adjusts the time for daylight saving.
The aforementioned Polar projection world clock of U.S. Pat. No. 5,146,436 to Wright, in providing a second indicator to represent local time, can be adjusted in observance of Daylight Saving Time. While Wright's design thus does provide a means to adjust the user's current geographical location time in accordance to Daylight Saving Time, it does not provide a means to correct the time within other time zones across the world which may also implement Daylight Saving Time.
In I. Smith's linear Mercator projection world time clock of U.S. Pat. No. 3,232,038, the position of the viewing window may be mechanically shifted parallel to the length of the scrolling band, thereby providing an avenue to correct a particular region's local time when Daylight Saving Time is in force. Again here, no general solution is provided to the issue of differing dates being used in various geographical regions and sub-regions for the application of Daylight Saving Time corrections.
Modern communications rely greatly on computers with electronically controlled presentation displays, and long distance telephony. In the case of computers, electronic messages are sent continuously by e-mail and other means over the Internet to destinations around the world. Similarly, long distance telephone call set-up may occur at any time of the day or night. When communicating to others across civil time zones, a person often needs a quick and convenient method for determining the local time at the target distant location.
It would be convenient to provide an electronic display for a clock incorporating a cartographic projection of the Earth. Further, it would be convenient to provide in such a display a means to accommodate changes due to Daylight Saving Time on a region-by-region basis, as well as other useful features. The present invention seeks to address such objectives by taking advantage of modern technology relating to electronically displayed images.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.